The primary function of the spanning-tree algorithm (STA) is to cut loops created
by redundant links in bridged networks. The Spanning-Tree Protocol
(STP) operates at Layer2 of the OSI model and, by the means of bridge protocol
data units (BPDUs) exchanged between bridges, elects the ports that will
eventually forward or block traffic. This protocol can fail in some specific cases
and troubleshooting the resulting situation can be very difficult, depending on
the design of the network. The most important part of troubleshooting is done
before the problem occurs....